In the field of digital data storage systems, most commercial computers employ Winchester-type disk drives to store application program software and related data. Digital data is stored in the form of magnetic energization on a series of concentric, closely spaced tracks partitioned on the surface of magnetizable rigid hard disks. The magnetizable disks typically include an active data storage region and an inactive region often termed the "landing zone." As the magnetic heads sweep across the active data storage region of the disk, digital data is applied to, and retrieved from, specified locations in response to address signals designating the desired storage locations.
When power is removed from the disk drive unit, typically associated with powering down the system, it is desirable to move the head positioner and magnetic heads to a position away from the active data storage region of the disks and over the "landing zone," typically provided on the inner portion or outer periphery of the disk. The process of moving the heads from the active region of the disk to the landing zone is widely known in the art as "parking" the heads. Once the heads are parked, it is desirable to latch the head positioner in the parked position, thus allowing the disk drive unit to be moved from one location to another and to withstand unintentional vibrations and shock without permitting the head positioner to leave the parked position which may otherwise result in damage to the magnetic heads and/or the storage disks.
To latch the head positioner in the parked position, many latching mechanisms employ a solenoid for engaging the head positioner. For example, in U.S. Pat. No. 4,985,793 (hereinafter the "'793 device"), a head positioner parking mechanism utilizes a continuously energized solenoid to hold a head positioner latching body out of engagement with the head positioner during normal disk drive operation. Continuous current applied to the solenoid during disk drive operation is required to generate a magnetic field of sufficient strength to overcome the attractive force between a permanent magnet structure and a magnetically permeable body included on the latching body. When the heads are to be parked, the solenoid is de-energized thereby permitting the latching body to swing into engagement with the head positioner as the magnetic field generated by the solenoid no longer overcomes the magnetic attraction between the latching body and permanent magnet structure. Unlatching of the '793 device requires energization of the solenoid to disengage the latching body from engagement with the head positioner. A disadvantage and limitation of the '793 device is that during operation of the disk drive, an electrical current needs to be continuously applied to the latching solenoid to keep the latching body retracted from the latched position. The required current generates heat in the solenoid which raises the operating ambient temperature of the disk drive unit. This, in turn, requires greater cooling and ventilation capability to offset the added heat load, or reduces the allowed power to the drive for other purposes. Moreover, mechanical and thermal stress, resulting from continuous thermal cycling of the solenoid, may cause early and unpredictable failure of the solenoid. Further, any failure of the solenoid apparatus during the unlatching procedure may cause unwanted latching of the head positioner in the parked position, thereby rendering the disk drive unit inoperable.
Other latching mechanisms, such as that disclosed in U.S. Pat. No. 4,989,108 (hereinafter the "'108 device"), employ an electro-mechanical latch wherein a locking lever is removed from its latching position when a current is applied to the electro-mechanical latch. Unlike the '793 device discussed hereinabove, a current need be applied to the solenoid of the '108 device only for moving the latch to release the head positioner from its parked position. The current may then be removed from the solenoid since the latch is held in a position which is non-interactive with the head positioner during normal disk drive operation. Amongst several of the inherent limitations of the '108 latching device, a significant deficiency involves the necessity of current during the unlatching procedure which must be applied to the latching solenoid in order to release the head positioner from the latched position. A failure of the solenoid apparatus or of the source supplying current to the solenoid will prohibit the head positioner from leaving the locked, parked position.
In other prior art devices, in which a current releases the latch and a mechanical hold feature allows current to be removed from the solenoid, the head positioner may need to have slight over-travel to trigger a hook mechanism which captures the head positioner in its parked position. This over-travel may require that some of the active data storage region be used in conjunction with this over-travel. Should the positioner fail to over travel, the hook mechanism will not engage the latch arm and the positioner will not be locked. Thus, such a scheme inherently wastes valuable disk storage space which reduces the overall storage capacity of the disk drive storage unit. Furthermore, such designs often suffer from excessive mechanical wear and unacceptable surface misalignments that cause the latch to be "sticky" and non-responsive to the unlatching mechanism.
Other head positioner latch mechanisms employ a magnet to accomplish the latching which results in an increase in complexity, an increase in the number of parts, and an increase of allocated chassis space required to house the latching mechanism. Adjustment tolerances between the latching mechanism and the head positioner apparatus often restrict the rotational range of the head positioner which translates into a reduction of effective active data storage surface area.
It is therefore an object of the present invention to overcome one or more of the disadvantages and limitations of the prior art discussed hereinabove. Accordingly, a principal object of the present invention is to provide a fail-safe, magnetically coupled head positioner latch having a simple, low cost design which includes a head positioner being held in the parked position by the magnetic coupling force between the latching mechanism and a permanent magnet structure, and which positively disengages from the latched position by operation of the head positioner upon initiation of normal head positioner activity.